IDR: Optical Imaging of High pH Dependent Degradation in Infrastructure Materials

New York University, New York NY

Investigators

Abstract

The objective of this Interdisciplinary Research (IDR) project is to study the use of advanced chemical sensing methods to measure the pH values in fresh and aging concrete. This work will be carried out for better understanding the acid/alkali dependent degradation phenomena in concrete structures by measurements with spatial and temporal resolution. The project's approach is specifically designed to study alkali-aggregate reactions in concrete, a major contributor to the premature deterioration of concrete structures. This strongly pH-dependent degradation reaction that takes place between the high pH media of hydrated Portland cement and the surrounding aggregate, produces expansive byproducts that result in the significant cracking of concrete. The proposed method will utilize a chemosensor made from a synthetic porphyrin-based sensor molecule that shows pH-specific changes in its optical spectrum when in contact with the alkali in concrete. The sensor molecule will be mixed into fresh concrete or applied onto fractured concrete surfaces to enable the measurement of pH levels. This research project will combine the expertise of a synthetic chemist for the design and synthesis of suitable pH-sensing chromophores, and the expertise of civil engineers to apply these chromophores in the study of alkali-silica reaction to concrete materials. If successful, the knowledge created through this grant will enable researchers to better understand the kinetics of alkali ions and the resulting distress in concrete structures. This understanding will ultimately enhance our capabilities in testing, mitigation, remediation, monitoring, early detection and service life prediction of concrete structures.